Question on String

[QuestionPlease]

I need help, I've got this porgram to count vowels in a string but how can I get it to count constants too?

Module Module1

    Sub Main()
        Dim vowel As String
        Dim count As Integer
        Dim str As String
        Dim index As Integer
        Dim cons As String
        vowel = "aeiou"
        Console.WriteLine("Enter a String")
        str = Console.ReadLine()
        For index = 1 To Len(str)
            If InStr(vowel, Mid(str, index, 1)) Then
                count = count + 1
            End If
        Next

        Console.WriteLine("There are " & count)
    End Sub

End Module